1. Field of the Invention
The present invention relates to reproduction apparatus; and to feeders for presenting an original, comprising a set of individual sheets, to such apparatus in a manner that facilitates collation of the reproductions into sets corresponding to the original. More specifically the invention relates to mechanisms for determining when the feeder malfunctions in the sense that it presents multiple sheets to the apparatus all at the same time. Feeders of this type include the so-called "recirculating" and "collating" document feeders, which have particular utility on convenience copiers.
2. Brief Description of the Prior Art
It is well known in the prior art to provide convenience copiers with document feeders that present the individual document sheets to the copier, one-after-another, in a manner suitable for producing collated copies without a sorter. Examples are disclosed in U.S. Pat. Nos. RE 27,976; 3,552,739; 3,556,511 and 3,709,595. It should be apparent from the above-mentioned types of structures that recirculating collating feeders can provide significant improvements in the total copying operation, especially in regard to the convenience and economics thereof. At the same time, however, it becomes more critical with such feeders that they operate repeatedly without malfunction, or at least that any serious malfunction be readily detectable and easily corrected. Collating feeders have not been made commercially available to date and, although the reasons are not known, it may be that the problems associated with malfunctions have played a part in delaying their introduction.
It also is known in the prior art to provide sensors and control apparatus for use in conjunction with copiers or document pg,3 feeders to prevent malfunctions or to act as alerting devices when one or more possible malfunctions occur. Noteable examples are disclosed in U.S. Pat. Nos. 3,249,354; 3,819,266; 3,882,308; 3,920,328; 3,928,772 and 3,932,755. Devices of this sort can be used with collating feeders and will prevent or detect certain malfunctions. Still, however, they are not entirely suitable for all purposes. A particularly difficult problem, for example, relates to malfunctions involving the simultaneous feeding of a plurality of sheets. The present invention is directed to this problem, and provides a particularly attractive solution that is not available from the prior art.